Fig. 1. G_s signaling pathway utilized in bioassay. The cyclic AMP-dependent response in oocytes co-expressing the zebrafish cDNA library and CFTR is activated by the binding of a ligand to a membrane receptor, causing the receptor to interact with a G protein (G_s). Upon dissociation from the heterotrimeric G-protein–receptor complex, the subunit activates adenylyl cyclase. This action leads to a cAMP signaling cascade, ending in the activation of CFTR. The output of this cascade is measured by electrophysiology and is the basis of the functional assay.